THIS invention relates to electrical power cables, and more specifically to a method of forming a seal between and around conductors of an electrical power cable particularly as a safety measure in potentially explosive applications. The invention also relates to a seal between and around conductors of an electrical power cable, and to a kit for forming such a seal.
Electrical power cables often are anchored to electrical apparatus with cable glands which prevent loads applied to the cable from being transferred to conductors inside the electrical apparatus. In some applications, for example in a flameproof (Ex d or E Ex d) apparatus, it is necessary to have a seal which retains the flameproof integrity of the apparatus. In other words, the seal must be capable, under explosion fault conditions, of preventing hot ignited material such as burning gas from escaping through the cable gland and/or through the cable itself.
Various different types of cable gland seals are known. For example, it is known to use an elastomeric sealing element in a cable gland seal for flameproof apparatus. Generally, these types of seals apply radial forces to the cable, and since the cable material is susceptible to plastic deformation and creep over time, these seals require careful design and have to be inspected periodically to ensure proper seal integrity. Also, since the insulated conductors of an electrical power cable do not always nest perfectly together, gaps between adjacent conductors can, in the event of an explosion inside the flameproof apparatus, form a path for hot gases and flames to exit the apparatus.
It is also known to form a seal in flameproof applications by introducing a settable compound between an inner surface of a cable gland and an outer sheath of an unarmoured cable or an inner sheath of an armoured cable. This type of seal does not apply radial forces to the cable and hence does not deform the cable sheath over time. However, these seals do not address the problem of gaps between adjacent, insulated conductors. In addition, these seals tend to be relatively difficult to inspect and, if the cable material is not compatible with the settable compound, proper adhesion between the seal and the cable may not be achieved.
Yet another known method of sealing a cable gland in flameproof applications is to cut back the outer insulation elements of the cable sufficiently to freely expose the individual, insulated conductors, to pass these conductors through a cable gland forming a cavity within the cable gland adjacent the conductors, and to place a settable compound into the cavity between and around the adjacent conductors. With this method, the compound typically is a two-part epoxy having a putty-type consistency which is pressed and kneaded into the cavity in the cable gland. Although this method can address problems associated with gaps between adjacent, insulated conductors and the application of radial forces to a cable, a major drawback is that the formation of a proper seal is relatively difficult and the quality of the seal is therefore dependent upon the expertise and dedication of the person mixing and placing the settable compound. Another drawback is that the settable compound does not always adhere well to the polymeric insulation material of the cable conductors.
It is an object of the present invention to provide a method of forming a seal on insulated conductors of an electrical power cable, particularly in flameproof applications, which is relatively easy to carry out, which is effective in sealing both between and around the insulated conductors, and which can form a proper seal with the polymeric material of the insulated conductors.